Ocular neovascularization: clarifying complex interactions

New insights in the mechanisms of opioid analgesia and tolerance: Ultramicronized palmitoylethanolamide down-modulates vascular endothelial growth factor-A in the nervous system

Growing evidence suggests that opioid analgesics modulate angiogenesis during pathophysiological processes. Vascular endothelial growth factor-A (VEGF-A) was recently proposed to be involved in pain development. To date, no anti-angiogenic drug is used for pain management. When administered in a bioavailable formulation, (i.e., ultramicronized) N-palmitoylethanolamine (PEA) delays the onset of morphine tolerance, improves morphine analgesic activity and reduces angiogenesis in in vivo models. This study aimed at investigating whether VEGF-A is involved in PEA-induced delay of morphine tolerance. The anti-VEGF-A monoclonal antibody bevacizumab was used as a reference drug. Preemptive and concomitant treatment with ultramicronized PEA delayed morphine tolerance and potentiated the analgesic effect of morphine, while counteracting morphine-induced increase of VEGF-A in the nervous system. Similar results were obtained when bevacizumab was administered together with morphine. Of note, bevacizumab showed an analgesic effect per se. In equianalgesic treatment regimens (obtained through increasing morphine doses and associating PEA), PEA resulted in lower expression of VEGF-A in dorsal root ganglia (DRG) and spinal cord compared to morphine alone. Similar results were observed for plasma levels of the soluble VEGF receptor 1 (sFLT-1). Moreover, in morphine-treated animals, two pain-related genes (i.e., Serpina3n and Eaat2) showed a more than 3-fold increase in their expression at spinal cord and DRG level, with the increase being significantly counteracted by PEA treatment. This study supports the hypothesis that the effects of PEA on morphine analgesia and tolerance may be mediated by the down-modulation of VEGF-A and sFLT-1 in the nervous system and plasma, respectively.

TAK1 blockade as a therapy for retinal neovascularization

Retinal neovascularization, or pathological angiogenesis in the retina, is a leading cause of blindness in developed countries. Transforming growth factor-β-activated kinase 1 (TAK1) is a mitogen-activated protein kinase kinase kinase (MAPKKK) activated by TGF-β1 and other proinflammatory cytokines. TAK1 is also a key mediator of proinflammatory signals and plays an important role in maintaining vascular integrity upon proinflammatory cytokine stimulation such as TNFα. However, its role in pathological angiogenesis, particularly in retinal neovascularization, remains unclear. Here, we investigate the regulatory role of TAK1 in human endothelial cells responding to inflammatory stimuli and in a rat model of oxygen-induced retinopathy (OIR) featured retinal neovascularization. Using TAK1 knockout human endothelial cells that subjected to inflammatory stimuli, transcriptome analysis revealed that TAK1 is required for activation of NFκB signaling and mediates its downstream gene expression related to endothelial activation and angiogenesis. Moreover, pharmacological inhibition of TAK1 by 5Z-7-oxozeaenol attenuated angiogenic activities of endothelial cells. Transcriptome analysis also revealed enrichment of TAK1-mediated NFκB signaling pathway in the retina of OIR rats and retinal neovascular membrane from patients with proliferative diabetic retinopathy. Intravitreal injection of 5Z-7-oxozeaenol significantly reduced hypoxia-induced inflammation and microglial activation, thus attenuating aberrant retinal angiogenesis in OIR rats. Our data suggest that inhibition of TAK1 may have therapeutic potential for the treatment of retinal neovascular pathologies.

Review of Machine Learning Applications Using Retinal Fundus Images

Automating screening and diagnosis in the medical field saves time and reduces the chances of misdiagnosis while saving on labor and cost for physicians. With the feasibility and development of deep learning methods, machines are now able to interpret complex features in medical data, which leads to rapid advancements in automation. Such efforts have been made in ophthalmology to analyze retinal images and build frameworks based on analysis for the identification of retinopathy and the assessment of its severity. This paper reviews recent state-of-the-art works utilizing the color fundus image taken from one of the imaging modalities used in ophthalmology. Specifically, the deep learning methods of automated screening and diagnosis for diabetic retinopathy (DR), age-related macular degeneration (AMD), and glaucoma are investigated. In addition, the machine learning techniques applied to the retinal vasculature extraction from the fundus image are covered. The challenges in developing these systems are also discussed.

Synergism effect of swimming exercise and genistein on the inflammation, oxidative stress, and VEGF expression in the retina of diabetic-ovariectomized rats

AIMS

Retinal neovascularization is one of the visual disorders during the postmenopausal period or types two diabetes. Physical activities and also phytoestrogens with powerful antioxidant features have been widely considered to improve nervous system diseases. Therefore, this study investigated the effects of genistein, swimming exercise, and their co-treatment on retina angiogenesis, oxidative stress, and inflammation in diabetic-ovariectomized rats.

MAIN METHODS

Wistar rats were randomly divided into six groups (n = 8 per group): sham, ovariectomized group (OVX), OVX + diabetes (OVX.D), OVX.D+ genistein (1 mg/kg, eight weeks; daily SC), OVX.D + exercise (eight weeks), and OVX.D+ genistein+exercise (eight weeks). At the end of 8 weeks, the retina was removed under anesthesia. The assessed effects of treatment were by measuring MiR-146a and miR-132 expression via RT-PCR, the protein levels of ERK, MMP-2, VEGF, and NF-κB via western blotting, inflammation, and oxidative stress markers levels via the Eliza.

KEY FINDINGS

The results showed miR-132, miR-146b, and MMP-2, NF-κB, ERK, VEGF, TNF-α, IL-1β proteins, and MDA factor in the OVX.D group were increased, but glutathione (GSH) was decreased in comparison with the sham and OVX groups. Both exercise and genistein treatment has reversed the disorder caused by diabetes. However, the combination of exercise and genistein was more effective than each treatment alone.

SIGNIFICANCE

It can be concluded that the interaction of exercise and genistein on microRNAs and their target protein was affected in the inflammation, stress oxidative, and extracellular matrix metalloproteinase pathways, can leading to a decrease in impairment of retinal neovascularization of the ovariectomized diabetic rats.

Application of Dimethyl Sulfoxide as a Therapeutic Agent and Drug Vehicle for Eye Diseases

Dimethyl sulfoxide (DMSO) is an amphipathic molecule widely used as a solvent for water-insoluble substances, cryopreserving, and cell-biological therapies. It has known properties as an inducer of cellular differentiation, a free radical scavenger, and a radioprotectant. In addition, DMSO is used for its various therapeutic and pharmaceutical properties, such as anti-inflammatory, local and systemic analgesic, antibacterial, antifungal, antiviral, and membrane penetration enhancement agents. DMSO treatment can be given orally, intravenously, or topically for a wide range of indications. The administration of DMSO exhibits favorable outcomes in human eye diseases with low to none observed ocular or systemic ocular toxicity. Nevertheless, DMSO is an essential and nonpatentable potential therapeutic agent that remains underexplored and ignored by pharmaceutical developers and ophthalmologists. This current review takes data from experimental and clinical studies that have been published to substantiate the potential therapeutic efficacy of DMSO and stimulate the research of its application in clinical ophthalmology. Given that DMSO is inexpensive, safe, and easily formulated into therapeutic medicinal products and conventional ophthalmological drugs, this compound should be further explored and studied in the treatment of a variety of acute and chronic ocular disorders.

Treatment Landscape of Macular Disorders in Indian Patients with the Advent of Razumab™ (World's First Biosimilar Ranibizumab): A Comprehensive Review

Ranibizumab is approved for the treatment of several macular disorders, including wet age-related macular degeneration (wet AMD), diabetic macular edema (DME), retinal vein occlusion (RVO) and myopic choroidal neovascularization (mCNV), among others. The unaffordability of the innovator ranibizumab among patients from developing countries such as India led to the development of the world’s first biosimilar ranibizumab, which is a cost-effective alternative that does not compromise efficacy and safety. Razumab™, developed and produced by Intas Pharmaceuticals Ltd., India, is the world’s first biosimilar of ranibizumab, and is approved in India for the treatment of various macular disorders, including wet AMD, DME, RVO and mCNV. The efficacy and safety of Razumab for the treatment of these macular disorders have been evaluated in both prospective and real-world retrospective studies. Razumab has shown an efficacy similar to that of the innovator ranibizumab, achieving improved visual acuity, as measured by the best corrected visual acuity, and reduction in the central macular thickness, leading to improved patient outcomes. The safety profile of Razumab is comparable to that of the innovator ranibizumab and is well tolerated without any new safety concerns. Here, we review the clinical and real-world data of Razumab in the treatment of macular disorders.

HIF Inhibition Therapy in Ocular Diseases

The uncontrolled growth of blood vessels is a major pathological factor in human eye diseases that can result in blindness. This effect is termed ocular neovascularization and is seen in diabetic retinopathy, age-related macular degeneration, glaucoma and retinopathy of prematurity. Current treatments for these diseases include laser photocoagulation, topical injection of corticosteroids, intravitreal injection of anti-vascular endothelial growth factor (anti-VEGF) agents and vitreoretinal surgery. Although strategies to inhibit VEGF have proved to be dramatically successful in some clinical studies, there remains the possibility of significant adverse effects regarding the blockade of crucial physiological roles of VEGF and the invasive nature of the treatments. Moreover, it is evident that other pro-angiogenic factors also play important roles in the development of these diseases, as seen in cases in which anti-VEGF therapies have failed. Therefore, new types of effective treatments are required. In this review, we discuss a promising strategy for the treatment of ocular neovascular diseases, i.e., the inhibition of hypoxia-inducible factor (HIF), a master regulator of angiogenesis. We also summarize promising recently investigated HIF inhibitors as treatments for ocular diseases. This review will facilitate more comprehensive approaches to understanding the protective aspects of HIF inhibition in the prevention of ocular diseases.

MicroRNAs in laser-induced choroidal neovascularization in mice and rats: their expression and potential therapeutic targets

Choroidal neovascularization characterizes wet age-related macular degeneration. Choroidal neovascularization formation involves a primarily angiogenic process that is combined with both inflammation and proteolysis. A primary cause of choroidal neovascularization pathogenesis is alterations in pro- and anti-angiogenic factors derived from the retinal pigment epithelium, with vascular endothelium growth factor being mainly responsible for both clinical and experimental choroidal neovascularization. MicroRNAs (miRNAs) which are short, non-coding, endogenous RNA molecules have a major role in regulating various pathological processes, including inflammation and angiogenesis. A review of recent studies with the mouse laser-induced choroidal neovascularization model has shown alterations in miRNA expression in choroidal neovascularization tissues and could be potential therapeutic targets for wet age-related macular degeneration. Upregulation of miR-505 (days 1 and 3 post-laser), miR-155 (day 14) occurred in retina; miR-342-5p (days 3 and 7), miR-126-3p (day 14) in choroid; miR-23a, miR-24, miR-27a (day 7) in retina/choroid; miR-505 (days 1 and 3) in retinal pigment epithelium/choroid; downregulation of miR-155 (days 1 and 3), miR-29a, miR-29b, miR-29c (day 5), miR-93 (day 14), miR-126 (day 14) occurred in retinal pigment epithelium/choroid. Therapies using miRNA mimics or inhibitors were found to decrease choroidal neovascularization lesions. Choroidal neovascularization development was reduced by overexpression of miR-155, miR-188-5p, miR-(5,B,7), miR-126-3p, miR-342-5p, miR-93, miR-126, miR-195a-3p, miR-24, miR-21, miR-31, miR-150, and miR-184, or suppression of miR-505, miR-126-3p, miR-155, and miR-23/27. Further studies are warranted to determine miRNA expression in mouse laser-induced choroidal neovascularization models in order to validate and extend the reported findings. Important experimental variables need to be standardized; these include the strain and age of animals, gender, number and position of laser burns to the eye, laser parameters to induce choroidal neovascularization lesions including wavelength, power, spot size, and duration.

Role of small interfering RNA (siRNA) in targeting ocular neovascularization: A review

Ocular neovascularization (NV) plays a central role in the pathogenesis of various ocular diseases including diabetic retinopathy, age-related macular degeneration, retinoblastoma, retinitis pigmentosa and may lead to loss of vision if not controlled in time. Several clinical trials elucidate the central role of vascular endothelial growth factor (VEGF) in the pathogenesis of the ocular neovascularization. The advent and extensive use of ocular anti-VEGF therapy heralded a new age in the treatment of retinal vascular and exudative diseases. RNA interference (RNAi) can be used to inhibit the in-vitro and in-vivo expression of specific genes and thus provides an extremely useful method for investigating gene activity with minimal toxicity. siRNA targeting VEGF overcomes many drawbacks associated with the conventional treatment available for the treatment of ocular neovascularization. However, delivery methods that protect the siRNA against degradation and are appropriate for long-term care will help increase the effectiveness of RNAi-based anti-VEGF ocular therapies. Several nanotechnology approaches have been explored by formulation scientists for delivery of siRNA to the eye; targeting particularly VEGF for the treatment of NV. This review mainly focuses on current updates in various pre-clinical and clinical siRNA strategies for targeting VEGF involved in the development of ocular neovascularization.

Phosphorylation of STAT3 and ERBB2 mediates hypoxia‑induced VEGF release in ARPE‑19 cells

Neovascularization in the retina can cause loss of vision. Vascular endothelial growth factor (VEGF) serves an important role in the pathogenesis of retinal vascular diseases. Hypoxia is a notable cause of VEGF release and both STAT3 and ERBB2 are known to be associated with VEGF. In addition, STAT3 and ERBB2 interact with each other. In the present study, it was hypothesized that signal transducer and activator of transcription 3 (STAT3) and erbB-2 receptor tyrosine kinase 2 (ERBB2) may be involved in the regulation of hypoxia-induced VEGF in the retina. Cells of the retinal pigment epithelium (RPE) are an important source of VEGF. Therefore, the RPE-derived human cell line ARPE-19 was exposed to hypoxia. Hypoxia-induced phosphorylation of STAT3 and ERBB2 in ARPE-19 cells was decreased by AG490, an inhibitor of Janus kinase 2, as were hypoxia-induced VEGF release and tube formation in human umbilical vein endothelial cells. Thus, phosphorylation of ERBB2 and STAT3 regulates hypoxia-induced VEGF release in ARPE-19 cells. The results of the present study suggested that inhibition of ERBB2 and STAT3-mediated pathways under hypoxia may represent a new strategy for treating retinal vascular disease.

Nanoscale delivery systems in treatment of posterior ocular neovascularization: strategies and potential applications

Pathologic posterior neovascularization of eye is a major cause of irreversible vision loss and limitations of therapeutics to be successfully delivered to back of the eye has been a main obstacle for its effective treatment. Current pharmacological treatment using anti-VEGF agents being delivered intravitreally are effective but complicated due to anatomical and physiological barriers, as well as administration of high and frequent doses. With expanding horizons of nanotechnology, it can be possible to formulate promising nanoscale delivery system to improve penetration and sustained the release of therapeutic in posterior segment of the eye. Taking into consideration advances in the field of nanoscale delivery systems, this special report focuses on emerging strategies and their applications for treatment of posterior ocular neovascularization.

Canonical Wnt Signaling Promotes Neovascularization Through Determination of Endothelial Progenitor Cell Fate via Metabolic Profile Regulation

Endothelial progenitor cells (EPCs) contribute to blood vessel formation. Canonical Wnt signaling plays an important role in physiological and pathological angiogenesis and EPC fate regulation. However, the mechanism for Wnt signaling to regulate EPC fate in neovascularization (NV) has not been clearly defined. Here, we showed that very low-density lipoprotein receptor knockout (Vldlr ^-/- ) mice, a model of ocular NV induced by Wnt signaling overactivation, have increased EPC numbers in the bone marrow, blood, and retina, as well as an elevated mitochondrial membrane potential indicating higher mitochondrial function of EPCs in the circulation. Isolated EPCs from Vldlr ^-/- mice showed overactivated Wnt signaling, correlating with increased mitochondrial function, mass, and DNA copy numbers, compared with WT EPCs. Our results also demonstrated that Wnt signaling upregulated mitochondrial biogenesis and function, while inhibiting glycolysis in EPCs, which further decreased EPC stemness and promoted EPCs to a more active state toward differentiation, which may contribute to pathologic vascular formation. Fenofibric acid, an active metabolite of fenofibrate, inhibited Wnt signaling and mitochondrial function in EPCs and decreased EPC numbers in Vldlr ^-/- mice. It also decreased mitochondrial biogenesis and reactive oxygen species production in Vldlr ^-/- EPCs, which may be responsible for its therapeutic effect on diabetic retinopathy. These findings demonstrated that Wnt signaling regulates EPC fate through metabolism, suggesting potential application of the EPC metabolic profile as predictor and therapeutic target for neovascular diseases. Stem Cells 2019;37:1331-1343.

Analog Derivatization of Cannabidiol for Improved Ocular Permeation

Purpose: Cannabidiol (CBD), active component of plant Cannabis sativa, has anti-inflammatory properties that could potentially help treat diabetic retinopathy-induced pain and inflammation. However, CBD is a lipophilic molecule making its topical delivery to back of the eye challenging. This study aims at improving ocular penetration of CBD by means of analog derivatization. Methods: Analogs were designed using various ligands, such as amino acids (AAs) and dicarboxylic acids (DCAs) and their combinations. Select analogs were screened in vitro with respect to their stability in ocular tissue homogenates. Based on in vitro stability, analogs were selected for in rabbits testing. Formulations containing these compounds were tested in rabbits to determine ocular tissue disposition of CBD and the analogs after topical application. The rabbits were sacrificed 90 min post-topical application and the aqueous humor, vitreous humor (VH), iris-ciliary bodies (IC), and retina-choroid (RC) were analyzed for CBD and analog content. Results: CBD-divalinate-dihemisuccinate (CBD-Di-VHS) and CBD-divalinate (CBD-Di-Val) were stable in the ocular tissue homogenates. Post-topical application, CBD and CBD-Di-Val analog levels were detected only in RC. Dosing of CBD-Di-VHS nanoemulsion generated analog levels both in the VH and in the RC, respectively. In contrast, post dosing of CBD-monovalinate-monohemisuccinate (CBD-Mono-VHS), both the analog and CBD were detected in the IC and RC. Conclusion: The analogs demonstrated superior penetration into ocular tissues in comparison with CBD. CBD-Di-VHS and CBD-Mono-VHS exhibited better permeation properties, possibly due to improved stability and physicochemical characteristics imparted by AA and DCA combination derivatives.

Is There A Role for Abscisic Acid, A Proven Anti-Inflammatory Agent, in the Treatment of Ischemic Retinopathies?

Ischemic retinopathies (IRs) are the main cause of severe visual impairment and sight loss, and are characterized by loss of blood vessels, accompanied by hypoxia, and neovascularization. Actual therapies, based on anti-vascular endothelial growth factor (VEGF) strategies, antioxidants or anti-inflammatory therapies are only partially effective or show some adverse side effects. Abscisic acid (ABA) is a phytohormone present in vegetables and fruits that can be naturally supplied by the dietary intake and has been previously studied for its benefits to human health. It has been demonstrated that ABA plays a key role in glucose metabolism, inflammation, memory and tumor growth. This review focuses on a novel and promising role of ABA as a potential modulator of angiogenesis, oxidative status and inflammatory processes in the retina, which are the most predominant characteristics of the IRs. Thus, this nutraceutical compound might shed some light in new therapeutic strategies focused in the prevention or amelioration of IRs-derived pathologies.

Oxidative stress upregulates Wnt signaling in human retinal microvascular endothelial cells through activation of disheveled

Abnormal retinal neovascularization associated with various retinopathies can result in irreversible vision loss. Although the mechanisms involved in this occurrence is unclear, increasing evidence suggests that aberrant Wnt signaling participates in the pathogenesis of abnormal neovascularization. Because Wnt signaling upregulation can be induced by oxidative stress through the activation of disheveled (DVL), a key molecule in the Wnt signaling pathway, we investigated whether oxidative stress can activate Wnt signaling and induce angiogenic phenotypes in human retinal microvascular endothelial cells (HRMECs). We found that increased Wnt signaling activity, as well as enhanced angiogenic phenotypes, such as tube formation and cell migration, were detected in the hydrogen peroxide-treated HRMECs. Moreover, these effects were effectively suppressed by a small-molecule Wnt inhibitor targeting the PDZ domain of DVL. Therefore, we propose that targeting abnormal Wnt signaling at the DVL level with a small-molecule inhibitor may represent a novel approach in retinal neovascularization treatment and prevention.

Opioids: Modulators of angiogenesis in wound healing and cancer

Opioids are potent drugs that are widely used to control wound or cancer pain. Increasing evidence suggest that opioids mediate clinically relevant effects that go beyond their classical role as analgesics. Of note, opioids appear to modulate angiogenesis - a process that is critical in wound healing and cancer progression. In this review, we focus on pro- and anti-angiogenic facets of opioids that arise from the activation of individual opioid receptors and the usage of individual concentrations or application routes. We overview the still incompletely elucidated mechanisms of these angiogenic opioid actions. Moreover, we describe plausible opioids effects, which - although not primarily studied in the context of vessel formation - may be related to the opioid-driven processes of angiogenesis. Finally we discuss the use of opioids as an innovative therapeutic avenue for the treatment of chronic wounds and cancer.

Identification of proteins associated with clinical and pathological features of proliferative diabetic retinopathy in vitreous and fibrovascular membranes

Purpose

To identify the protein profiles in vitreous associated with retinal fibrosis, angiogenesis, and neurite formation in epiretinal fibrovascular membranes (FVMs) in patients with proliferative diabetic retinopathy (PDR).

Methods

Vitreous samples of 5 non-diabetic control patients with vitreous debris and 7 patients with PDR membranes were screened for 507 preselected proteins using the semi-quantitative RayBio® L-series 507 antibody array. From this array, 60 proteins were selected for a custom quantitative antibody array (Raybiotech, Human Quantibody® array), analyzing 7 control patients, 8 PDR patients with FVMs, and 5 PDR patients without FVMs. Additionally, mRNA levels of proteins of interest were measured in 10 PDR membranes and 11 idiopathic membranes and in retinal tissues and cells to identify possible sources of protein production.

Results

Of the 507 proteins screened, 21 were found to be significantly elevated in PDR patients, including neurogenic and angiogenic factors such as neuregulin 1 (NRG1), nerve growth factor receptor (NGFR), placental growth factor (PlGF) and platelet derived growth factor (PDGF). Angiopoietin-2 (Ang2) concentrations were strongly correlated to the degree of fibrosis and the presence of FVMs in patients with PDR. Protein correlation analysis showed PDGF to be extensively co-regulated with other proteins, including thrombospondin-1 and Ang2. mRNA levels of glial-derived and brain/derived neurotrophic factor (GDNF and BDNF) were elevated in PDR membranes. These results were validated in a second study of 52 vitreous samples of 32 PDR patients and 20 control patients.

Conclusions

This exploratory study reveals protein networks that potentially contribute to neurite outgrowth, angiogenesis and fibrosis in the formation of fibrovascular membranes in PDR. We identified a possible role of Ang2 in fibrosis and the formation of FVMs, and of the neurotrophic factors NRG1, PDGF and GDNF in neurite growth that occurs in all FVMs in PDR.

Physiological and ecological implications of ocean deoxygenation for vision in marine organisms

Climate change has induced ocean deoxygenation and exacerbated eutrophication-driven hypoxia in recent decades, affecting the physiology, behaviour and ecology of marine organisms. The high oxygen demand of visual tissues and the known inhibitory effects of hypoxia on human vision raise the questions if and how ocean deoxygenation alters vision in marine organisms. This is particularly important given the rapid loss of oxygen and strong vertical gradients in oxygen concentration in many areas of the ocean. This review evaluates the potential effects of low oxygen (hypoxia) on visual function in marine animals and their implications for marine biota under current and future ocean deoxygenation based on evidence from terrestrial and a few marine organisms. Evolutionary history shows radiation of eye designs during a period of increasing ocean oxygenation. Physiological effects of hypoxia on photoreceptor function and light sensitivity, in combination with morphological changes that may occur throughout ontogeny, have the potential to alter visual behaviour and, subsequently, the ecology of marine organisms, particularly for fish, cephalopods and arthropods with 'fast' vision. Visual responses to hypoxia, including greater light requirements, offer an alternative hypothesis for observed habitat compression and shoaling vertical distributions in visual marine species subject to ocean deoxygenation, which merits further investigation.This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'.

Roles of exosomes in the normal and diseased eye

Exosomes are nanometer-sized vesicles that are released by cells in a controlled fashion and mediate a plethora of extra- and intercellular activities. Some key functions of exosomes include cell-cell communication, immune modulation, extracellular matrix turnover, stem cell division/differentiation, neovascularization and cellular waste removal. While much is known about their role in cancer, exosome function in the many specialized tissues of the eye is just beginning to undergo rigorous study. Here we review current knowledge of exosome function in the visual system in the context of larger bodies of data from other fields, in both health and disease. Additionally, we discuss recent advances in the exosome field including use of exosomes as a therapeutic vehicle, exosomes as a source of biomarkers for disease, plus current standards for isolation and validation of exosome populations. Finally, we use this foundational information about exosomes in the eye as a platform to identify areas of opportunity for future research studies.

miR-126 Regulation of Angiogenesis in Age-Related Macular Degeneration in CNV Mouse Model

miR-126 has recently been implicated in modulating angiogenic factors in vascular development. Understandings its biological significance might enable development of therapeutic interventions for diseases like age-related macular degeneration (AMD). We aimed to determine the role of miR-126 in AMD using a laser-induced choroidal neovascularization (CNV) mouse model. CNV was induced by laser photocoagulation in C57BL/6 mice. The CNV mice were transfected with scrambled miR or miR-126 mimic. The expression of miR-126, vascular endothelial growth factor-A (VEGF-A), Kinase insert domain receptor (KDR) and Sprouty-related EVH1 domain-containing protein 1 (SPRED-1) in ocular tissues were analyzed by qPCR and Western blot. The overexpression effects of miR-126 were also proven on human microvascular endothelial cells (HMECs). miR-126 showed a significant decrease in CNV mice (p < 0.05). Both mRNA and protein levels of VEGF-A, KDR and SPRED-1 were upregulated with CNV; these changes were ameliorated by restoration of miR-126 (p < 0.05). CNV was reduced after miR-126 transfection. Transfection of miR-126 reduced the HMECs 2D-capillary-like tube formation (p < 0.01) and migration (p < 0.01). miR-126 has been shown to be a negative modulator of angiogenesis in the eye. All together these results high lights the therapeutic potential of miR-126 suggests that it may contribute as a putative therapeutic target for AMD in humans.

Bloodstream-To-Eye Infections Are Facilitated by Outer Blood-Retinal Barrier Dysfunction

The blood-retinal barrier (BRB) functions to maintain the immune privilege of the eye, which is necessary for normal vision. The outer BRB is formed by tightly-associated retinal pigment epithelial (RPE) cells which limit transport within the retinal environment, maintaining retinal function and viability. Retinal microvascular complications and RPE dysfunction resulting from diabetes and diabetic retinopathy cause permeability changes in the BRB that compromise barrier function. Diabetes is the major predisposing condition underlying endogenous bacterial endophthalmitis (EBE), a blinding intraocular infection resulting from bacterial invasion of the eye from the bloodstream. However, significant numbers of EBE cases occur in non-diabetics. In this work, we hypothesized that dysfunction of the outer BRB may be associated with EBE development. To disrupt the RPE component of the outer BRB in vivo, sodium iodate (NaIO₃) was administered to C57BL/6J mice. NaIO₃-treated and untreated mice were intravenously injected with 10⁸ colony forming units (cfu) of Staphylococcus aureus or Klebsiella pneumoniae. At 4 and 6 days postinfection, EBE was observed in NaIO₃-treated mice after infection with K. pneumoniae and S. aureus, although the incidence was higher following S. aureus infection. Invasion of the eye was observed in control mice following S. aureus infection, but not in control mice following K. pneumoniae infection. Immunohistochemistry and FITC-dextran conjugate transmigration assays of human RPE barriers after infection with an exoprotein-deficient agr/sar mutant of S. aureus suggested that S. aureus exoproteins may be required for the loss of the tight junction protein, ZO-1, and for permeability of this in vitro barrier. Our results support the clinical findings that for both pathogens, complications which result in BRB permeability increase the likelihood of bacterial transmigration from the bloodstream into the eye. For S. aureus, however, BRB permeability is not required for the development of EBE, but toxin production may facilitate EBE pathogenesis.

Blood-Retinal Barrier Compromise and Endogenous Staphylococcus aureus Endophthalmitis

PURPOSE

To test the hypothesis that blood-retinal barrier compromise is associated with the development of endogenous Staphylococcus aureus endophthalmitis.

METHODS

To compromise the blood-retinal barrier in vivo, streptozotocin-induced diabetes was induced in C57BL/6J mice for 1, 3, or 5 months. Diabetic and age-matched nondiabetic mice were intravenously injected with 108 colony-forming units (cfu) of S. aureus, a common cause of endogenous endophthalmitis in diabetics. After 4 days post infection, electroretinography, histology, and bacterial counts were performed. Staphylococcus aureus-induced alterations in in vitro retinal pigment epithelial (RPE) cell barrier structure and function were assessed by anti-ZO-1 immunohistochemistry, FITC-dextran conjugate diffusion, and bacterial transmigration assays.

RESULTS

We observed one bilateral infection in a control, nondiabetic animal (mean = 1.54 × 103 ± 1.78 × 10² cfu/eye, 7% incidence). Among the 1-month diabetic mice, we observed culture-confirmed unilateral infections in two animals (mean = 5.54 × 10² ± 7.09 × 10² cfu/eye, 12% incidence). Among the 3-month diabetic mice, infections were observed in 11 animals, three with bilateral infections (mean = 2.67 × 10² ± 2.49 × 10² cfu/eye, 58% incidence). Among the 5-month diabetic mice, we observed infections in five animals (mean = 7.88 × 10² ± 1.08 × 10³ cfu/eye, 33% incidence). In vitro, S. aureus infection reduced ZO-1 immunostaining and disrupted the barrier function of cultured RPE cells, resulting in diffusion of fluorophore-conjugated dextrans and transmigration of live bacteria across a permeabilized RPE barrier.

CONCLUSIONS

Taken together, these results indicated that S. aureus is capable of inducing blood-retinal barrier permeability and causing endogenous bacterial endophthalmitis in normal and diabetic animals.

High Glucose and Glucose Deprivation Modulate Müller Cell Viability and VEGF Secretion

PURPOSE

Diabetic retinopathy is manifested by excessive angiogenesis and high level of vascular endothelial growth factor (VEGF) in the eye.

METHODS

Human (MIO-M1) and rat (rMC-1) Müller cells were treated with 0, 5.5, or 30mM glucose for 24 hours. Viable cell counts were obtained by Trypan Blue Dye Exclusion Method. ELISA was used to determine VEGF levels in cell medium.

RESULTS

Compared to 24 hour treatment by 5.5mM glucose, MIO-M1 and rMC-1 in 30mM glucose increased in viable cell number by 38% and 24% respectively. In contrast, viable cells in 0mM glucose decreased by 28% and 50% respectively. Compared to 5.5mM, MIO-M1 and rMC-1 in 30mM glucose had increased levels of VEGF in cell medium (pg/ml by 24% and 20%) and also VEGF concentration in cells held in 0mM increased by 47% and 10% respectively. In both MIO-M1 and rMC-1, the amount of VEGF secreted per cell increased by about 100% when glucose was changed from 5.5 to 0mM but decreased slightly (17% in MIO-M1 and 11% in rMC-1) when glucose was increased from 5.5 to 30mM.

CONCLUSIONS

Our results show that MIO-M1 and rMC-1 are highly responsive to changes in glucose concentrations. 30mM compared to 5.5mM significantly increased cell viability but induced a significant change in VEGF secretion per cell in rMC-1 only. At 0, 5.5, and 30mM glucose, MIO-M1 secreted about 5-7-fold higher level of VEGF (pg/cell) than rMC-1. The mechanism of glucose-induced changes in rMC-1 and MIO-M1 cell viability and VEGF secretion remains to be elucidated.

Resveratrol suppresses vascular endothelial growth factor secretion via inhibition of CXC-chemokine receptor 4 expression in ARPE-19 cells

The present study characterizes the effects of resveratrol (Res) on vascular endothelial growth factor (VEGF) secretion in retinal pigment epithelial (RPE) cells. ARPE-19 cells were treated with CoCl2, a hypoxia mimetic agent. CoCl2 treatment increased protein levels of hypoxia inducible factor-1α (HIF-1α) and CXC-chemokine receptor 4 (CXCR4), and secretion of VEGF. To confirm the effects of Res on VEGF secretion, the human umbilical vein endothelial cell tube formation assay was performed with conditioned medium from Res-treated ARPE-19 cells. The well-known antioxidant Res effectively blocked these effects and reduced phosphorylation of nuclear factor (NF)-κB, an upstream activator of CXCR4. Furthermore, Res also suppressed VEGF secretion induced by SDF-1, a ligand of CXCR4. Conditioned medium from Res-treated ARPE-19 cells clearly suppressed tube formation compared with hypoxia-treated conditioned medium. The results demonstrated that Res inhibited the hypoxia mimetic CoCl2-induced expression of VEGF in ARPE-19 cells. Res suppressed CXCR4 expression through decreased phosphorylation of NF-κB, resulting in downregulation of VEGF secretion.

Endostar inhibits hypoxia-induced cell proliferation and migration via the hypoxia-inducible factor-1α/vascular endothelial growth factor pathway in vitro

Endostar, a recombinant human endostatin, is recognized as one of the most effective angiogenesis inhibitors. The angiogenesis inhibitory effects of Endostar suggest a possible beneficial role of Endostar in choroidal neovascularization (CNV), which is predominantly induced by hypoxia. In our previous study, it was reported that Endostar may inhibit the proliferation and migration of RF/6A choroid‑retinal endothelial cells. However, the inhibitory effect of Endostar on hypoxia‑induced cell proliferation and migration in RF/6A cells has not yet been elucidated. Therefore, the present study investigated the effect of Endostar on hypoxia‑induced cell proliferation and migration in RF/6A cells and the possible mechanisms underlying this effect. Under chemical hypoxia conditions, cell viability was increased to 114.9±10.1 and 123.6±9.6% in cells treated with 100 and 200 µm CoCl2, respectively, compared with the control (P<0.01). Pretreatment with 10‑100 µg/ml Endostar significantly inhibited CoCl2‑induced cell proliferation (P<0.05), and pre‑treatment with 10 µg/ml Endostar for 24, 48 and 96 h attenuated CoCl2‑promoted cell migration by 60.5, 48.3 and 39.6%, respectively, compared with the control (P<0.001). In addition, pretreatment with 10 µg/ml Endostar reversed the cell cycle arrest at S phase and the increased expression of hypoxia‑inducible factor‑1α (HIF‑1α) and vascular endothelial growth factor (VEGF) mRNA in RF/6A cells treated with 200 µM CoCl2. These data indicate that Endostar inhibited CoCl2‑induced hypoxic proliferation and migration, and limited cell cycle progression in vitro possibly through the HIF‑1α/VEGF pathway.

Anti-angiogenic effects of a mutant endostatin: a new prospect for treating retinal and choroidal neovascularization

Purpose

Pathological fundus angiogenesis is a major cause of vision loss in retina diseases. Endostatin, a C-terminal fragment of collagen XVIII, is an endogenous anti-angiogenic protein. The present study aimed to investigate the in vitro and in vivo anti-angiogenic properties of two proteins: an N-terminal H1D/H3D mutant endostatin (M-ES) and a polyethylene glycol propionaldehyde (PEG) covalent M-ES (PEG-M-ES).

Methods

M-ES and PEG-M-ES properties were characterized in vitro using a zinc ion binding assay and a stability test. Activity assays, including migration, proliferation, and tube formation assays, were performed with human retinal microvascular endothelial cells (HRMECs) and human umbilical vein endothelial cells (HUVECs). Mouse oxygen-induced retinopathy (OIR) and choroidal neovascularization (CNV) models were used to evaluate in vivo anti-angiogenic effects. In addition, a rabbit model was used to study the retinal pharmacokinetic profile following an intravitreal injection.

Results

The results indicated that the H1D/H3D mutations of endostatin reduced the zinc binding capacity of M-ES and facilitated PEG covalent binding. PEG-M-ES was more stable and persisted longer in the retina compared with M-ES. The in vitro studies demonstrated that M-ES and PEG-M-ES inhibited HRMEC and HUVEC proliferation, migration, and tube formation more efficiently than ES. In vivo, a single intravitreal injection of M-ES and PEG-M-ES significantly decreased neovascularization in both the OIR and CNV animal models.

Conclusion

The present study demonstrated for the first time that PEG-M-ES exhibits a long-term inhibitory effect on neovascularization in vitro and in vivo. These data suggest that PEG-M-ES may represent an innovative therapeutic strategy to prevent fundus neovascularization.

Angiogenesis and its therapeutic opportunities

Angiogenesis plays critical roles in human physiology that range from reproduction and fetal growth to wound healing and tissue repair. The sophisticated multistep process is tightly regulated in a spatial and temporal manner by "on-off switch signals" between angiogenic factors, extracellular matrix components, and endothelial cells. Uncontrolled angiogenesis may lead to several angiogenic disorders, including vascular insufficiency (myocardial or critical limb ischemia) and vascular overgrowth (hemangiomas, vascularized tumors, and retinopathies). Thus, numerous therapeutic opportunities can be envisaged through the successful understanding and subsequent manipulation of angiogenesis. Here, we review the clinical implications of angiogenesis and discuss pro- and antiangiogenic agents that offer potential therapy for cancer and other angiogenic diseases.

The diabetic ocular environment facilitates the development of endogenous bacterial endophthalmitis

PURPOSE

We tested the hypothesis that changes in the diabetic ocular environment facilitate the development of endogenous bacterial endophthalmitis (EBE).

METHODS

C57BL/6J mice were rendered diabetic with streptozotocin (STZ) for 1, 3, or 5 months' duration. Diabetic and age-matched nondiabetic mice were tail vein-injected with 10(8) CFU of Klebsiella pneumoniae, a common cause of EBE in diabetics. After either 2 or 4 days postinfection, the EBE incidence was assessed by electroretinography, histology, bacterial counts, and myeloperoxidase ELISAs. Blood-retinal barrier (BRB) permeability in uninfected diabetic mice also was determined.

RESULTS

No cases of EBE were observed among the 1-month diabetic group. Extending the time from diabetes induction to 3 months resulted in a 23.8% EBE incidence after 2 days, and a 22% incidence after 4 days. The incidence of EBE increased to 27% in the 5-month diabetic group. Infected eyes had an average 8.01 × 10(2) and 6.19 × 10(4) CFU/eye for the 3- and 5-month diabetic groups, respectively. There was no significant difference in BRB permeability between control and 1-month uninfected diabetic mice. However, 3- and 5-month diabetic mice had significantly greater BRB permeability than control mice. These results suggested that increasing the time from STZ diabetes induction to 3 and 5 months resulted in an ocular environment more conducive to the development of EBE.

CONCLUSIONS

These results demonstrated a correlation between an increase in BRB permeability and an increase in EBE incidence, supporting the hypothesis that diabetic ocular changes contribute to the development of EBE.

Reduced retinal microvascular density, improved forepaw reach, comparative microarray and gene set enrichment analysis with c-jun targeting DNA enzyme

Retinal neovascularization is a critical component in the pathogenesis of common ocular disorders that cause blindness, and treatment options are limited. We evaluated the therapeutic effect of a DNA enzyme targeting c-jun mRNA in mice with pre-existing retinal neovascularization. A single injection of Dz13 in a lipid formulation containing N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl-sulfate and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine inhibited c-Jun expression and reduced retinal microvascular density. The DNAzyme inhibited retinal microvascular density as effectively as VEGF-A antibodies. Comparative microarray and gene expression analysis determined that Dz13 suppressed not only c-jun but a range of growth factors and matrix-degrading enzymes. Dz13 in this formulation inhibited microvascular endothelial cell proliferation, migration and tubule formation in vitro. Moreover, animals treated with Dz13 sensed the top of the cage in a modified forepaw reach model, unlike mice given a DNAzyme with scrambled RNA-binding arms that did not affect c-Jun expression. These findings demonstrate reduction of microvascular density and improvement in forepaw reach in mice administered catalytic DNA.

DEHP effects on retinal vessels in newborn rats: a qualitative and quantitative analysis

Di-(2-ethylhexyl)-phthalate (DEHP), employed in polyvinyl chloride fabrication and released by endotracheal tubes, is known to cause alterations to several mammalian tissues, markedly in immature animals. The high incidence and severity of bronchopulmonary dysplasia and retinopathy in preterm babies submitted to endotracheal intubation prompted us to investigate the effects of DEHP in lung and retina perinatal development. We previously demonstrated that in rats delivered and breast-fed by DEHP-treated mothers lung alveolarisation is severely impaired. In the present research, the maturation of retinal vessels was studied in (a) flat-mounted retinas obtained after intracardiac injection of FITC-conjugated dextran, (b) flat-mounted retinas incubated with FITC-conjugated Bandeira simplicifolia isolectin B4, marker of vascular endothelial cells, and (c) eyecup sections incubated with biotinylated IB4 and revealed by ABC. DEHP-induced vascular alterations mainly affected the superficial plexus, where the radial vessels showed non-perfused as well as remarkably dilated and branched segments, capillary net appeared coarsely arranged and locally absent; periarteriolar capillary-free regions were still found in 14-day-old animals. This extensive vascular remodelling and generally the high responsiveness to DEHP shown by the immature rat retina confirm previous hypothesis that the phthalate released by PVC medical devices remarkably affects perinatal development of several tissues in different body districts.

Intraretinal pH in Diabetic Cats

PURPOSE

To examine intraretinal extracellular H+ concentration([H+]o) in diabetic cats.

METHODS

Double-barreled H+-selective microelectrodes were used to measure [H+]o as a function of retinal depth ([H+]o profiles) in four cats with different stages of diabetic retinopathy. Profiles from "normal"and "damaged" areas of the retina were compared to profiles previously obtained from healthy cats.

RESULTS

In the healthy retina, [H+]o is generally highest in the middle of the retina and decreases toward the choroid and the vitreous. In 48 % of the profiles from diabetic animals with visible retinopathy, the inner retinal gradient was reversed so that the vitreous was more acidic than the middle of the retina. The profiles with reversed inner retinal gradients were classified as damaged. On the average, the inner retina tended to be 0.07-0.08 pH units more acidic in diabetic animals than in healthy normoglycemic animals, but of similar acidity to healthy hyperglycemic animals. In areas with damaged inner retinal gradients, net H+ production in the outer retina was also impaired.

CONCLUSIONS

While the number of animals is small, we conclude that the [H+](O) distribution varied from normal to damaged in the same retina. Diabetes seems to lead to an acidification of the inner retina that appears to be at least partly related to hyperglycemia and which may be important in the progression of retinopathy.

Angiostatin and integrin ?v?3 in the feline, bovine, canine, equine, porcine and murine retina and cornea

PURPOSE

Angiogenesis is tightly controlled in the ocular tissues of domestic animals but its mechanisms are not fully understood. This is largely because of insufficient data on the expression of molecules that impact angiogenesis. Because angiostatin and one of its receptors integrin alphavbeta3 inhibit and promote angiogenesis, respectively, we hypothesized that the normal retina and cornea of domestic animals would express angiostatin but not integrin alphavbeta3.

PROCEDURE

Normal eyes of the cat, cow, dog, horse, pig and rat were evaluated for angiostatin and integrin alphavbeta3 by light and electron immunocytochemistry and estern blots.

RESULTS

Angiostatin was detected in the corneal epithelium of the cat, dog, horse, pig and rat, but was not found in cow corneal epithelium. Angiostatin was localized in the nerve fiber layer, ganglion cell layer, inner and outer plexiform layers, and the photoreceptor layer of the cat, cow, dog and rat. Horse and pig retinas showed additional staining in the matrix of the inner nuclear layer. Immunogold electron microscopy further confirmed angiostatin in cat retina. Western blots showed angiostatin in corneal and retinal homogenates. Integrin alphavbeta3 was absent in cornea and retina of all the species studied.

CONCLUSION

These data show that angiostatin, an inhibitor of angiogenesis, is present while integrin alphavbeta3, which promotes angiogenesis, is absent in normal cornea and retina of the domestic animals in this study with the exception being angiostatin absence in cow corneal epithelium. Therefore, angiostatin may contribute to the anti-angiogenic environment in the normal domestic animal eye while its absence in the cow may contribute to greater propensity for corneal vascularization. Because integrin alphavbeta3 is one of the receptors for angiostatin, its absence may prevent angiostatin from killing normal retinal and corneal cells.

Coordinated Expression of Ets-1, pERK1/2, and VEGF in Retina of Streptozotocin-Induced Diabetic Rats

PURPOSE

To investigate the role played by E26 transformation-specific-1 (Ets-1), a transcription factor, and extracellular signal-regulated kinase 1/2 (ERK1/2) in the expression of vascular endothelial growth factor (VEGF), and the interaction of Ets-1 and ERK1/2 in the retina of diabetic rats.

METHODS

Diabetes was induced in rats by an intraperitoneal injection of streptozotocin (STZ). To follow the time course in the expression of Ets-1, phosphorylated ERK1/2 (pERK1/2), and VEGF, rats were killed at 1, 2, 4, and 8 weeks after the injection of STZ, and total proteins were extracted from the isolated retinas. An adenovirus vector encoding dominant-negative Ets-1 and an inhibitor of PD98059 was injected intravitreally to investigate the effects of Ets-1 blockade and ERK1/2 inhibition on the expression of VEGF. Four weeks after the first intravitreal injection, total proteins and total RNA were extracted from the retinas for Western blot and Northern blot analyses.

RESULTS

The expression of Ets-1, pERK1/2, and VEGF in the retina increased in a time-dependent manner after STZ injection. The phosphorylation of ERK1/2 and protein level of VEGF were significantly reduced following intravitreal Ets-1. Inhibition of ERK1/2 phosphorylation resulted in a significant reduction in the expression of Ets-1 and the level of VEGF protein.

CONCLUSIONS

These results indicate that in the retina of STZ-induced diabetic rats: (1) the alterations of Ets-1, pERK1/2, and VEGF are approximately synchronized; (2) the phosphorylation of ERK1/2 is regulated by the expression of Ets-1; (3) the production of Ets-1 protein is dependent on the ERK1/2 pathway, and (4) the protein level of VEGF is regulated by both Ets-1 expression and ERK1/2 phosphorylation. We propose that VEGF, Ets-1, and ERK1 act synergistically in the development of diabetic retinopathy.

Delta-like ligand 4 (Dll4) is induced by VEGF as a negative regulator of angiogenic sprouting

Genetic deletion studies have shown that haploinsufficiency of Delta-like ligand (Dll) 4, a transmembrane ligand for the Notch family of receptors, results in major vascular defects and embryonic lethality. To better define the role of Dll4 during vascular growth and differentiation, we selected the postnatal retina as a model because its vasculature develops shortly after birth in a highly stereotypic manner, during which time it is accessible to experimental manipulation. We report that Dll4 expression is dynamically regulated by VEGF in the retinal vasculature, where it is most prominently expressed at the leading front of actively growing vessels. Deletion of a single Dll4 allele or pharmacologic inhibition of Dll4/Notch signaling by intraocular administration of either soluble Dll4-Fc or a blocking antibody against Dll4 all produced the same set of characteristic abnormalities in the developing retinal vasculature, most notably enhanced angiogenic sprouting and increased endothelial cell proliferation, resulting in the formation of a denser and more highly interconnected superficial capillary plexus. In a model of ischemic retinopathy, Dll4 blockade also enhanced angiogenic sprouting and regrowth of lost retinal vessels while suppressing ectopic pathological neovascularization. Our data demonstrate that Dll4 is induced by VEGF as a negative feedback regulator and acts to prevent overexuberant angiogenic sprouting, promoting the timely formation of a well differentiated vascular network.

The expression of nuclear factor kappa B in inflammation-induced rat corneal neovascularization

PURPOSE

To investigate the involvement of the nuclear-transfactor-kappa B (NF-kappa B) in the rat model of inflammation-induced corneal neovascularization (CNV).

METHODS

The CNV model in Sprague-Dawley rats was induced by alkaline cauterization of the central cornea. The corneas were examined by a slit lamp microscope. NF-kappa B was assayed by Western blot. Vascular endothelial growth factor (VEGF) protein was evaluated by immunohistochemistry. VEGF mRNA levels were determined by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Morphologically, the CNV was shown on the second day after cautery. In corneas after cautery, NF-kappa B protein increased 6 hours after cautery, peaked 4 days after cautery, and decreased to near baseline by day 14. VEGF protein and mRNA increased gradually in the early stage after cautery, reached the highest level on the fourth day, and then decreased to near baseline slowly after 7 days.

CONCLUSIONS

The activated NF-kappa B was up-regulated in the early stage of CNV of rat induced by cauterization, which suggests it may participate in the pathogenesis of wound healing, inflammation, and neovascularization processes in the cornea.

Microphthalmia, persistent hyperplastic hyaloid vasculature and lens anomalies following overexpression of VEGF-A188 from the alphaA-crystallin promoter

PURPOSE

During growth of the embryonic eye, dose- and site-specific expression of heparin-binding growth factors is critical for the formation of an appropriate vascular supply. Overexpression of vascular endothelial growth factor-A(188) (VEGF-A(188)), a strongly heparin-binding, endothelial-specific mitogen, leads to severe disturbance of vascular and overall ocular morphology. This study aimed to evaluate the effects of VEGF-A(188) overexpression on growth of ocular tissue components.

METHODS

Stereological and immunohistochemical methods were employed to identify the vascular profiles, ocular tissue proportions, and cell types in VEGF-A(188) transgenic mice and compare them with wild-type mice.

RESULTS

In VEGF-A(188) transgenic mice, both lens tissue and total ocular volume were reduced, whereas cross-sectional areas of hyaloid blood vessels, retina, iris, and optic stalk tissues were significantly increased compared to wild-type mice. Endothelial and pericyte cell numbers in the hyaloid vasculature of transgenic mice were increased three fold, with pericytes assuming their characteristic extraluminal position.

CONCLUSIONS

Overexpression of VEGF-A(188) in the murine lens results in microphthalmia, in addition to hypertrophy and persistence of the hyaloid vasculature. This is similar to the human disorder persistent hyperplastic primary vitreous (PHPV). The murine model is a useful, experimental paradigm for investigation of this condition.

Neuroprotective and blood-retinal barrier-preserving effects of cannabidiol in experimental diabetes

Diabetic retinopathy is characterized by blood-retinal barrier (BRB) breakdown and neurotoxicity. These pathologies have been associated with oxidative stress and proinflammatory cytokines, which may operate by activating their downstream target p38 MAP kinase. In the present study, the protective effects of a nonpsychotropic cannabinoid, cannabidiol (CBD), were examined in streptozotocin-induced diabetic rats after 1, 2, or 4 weeks. Retinal cell death was determined by terminal dUTP nick-end labeling assay; BRB function by quantifying extravasation of bovine serum albumin-fluorescein; and oxidative stress by assays for lipid peroxidation, dichlorofluorescein fluorescence, and tyrosine nitration. Experimental diabetes induced significant increases in oxidative stress, retinal neuronal cell death, and vascular permeability. These effects were associated with increased levels of tumor necrosis factor-alpha, vascular endothelial growth factor, and intercellular adhesion molecule-1 and activation of p38 MAP kinase, as assessed by enzyme-linked immunosorbent assay, immunohistochemistry, and/or Western blot. CBD treatment significantly reduced oxidative stress; decreased the levels of tumor necrosis factor-alpha, vascular endothelial growth factor, and intercellular adhesion molecule-1; and prevented retinal cell death and vascular hyperpermeability in the diabetic retina. Consistent with these effects, CBD treatment also significantly inhibited p38 MAP kinase in the diabetic retina. These results demonstrate that CBD treatment reduces neurotoxicity, inflammation, and BRB breakdown in diabetic animals through activities that may involve inhibition of p38 MAP kinase.

An eye on insulin

Diabetic retinopathy, the most frequent complication of diabetes and leading cause of vision loss, involves vascular and neural damage in the retina. Insulin and IGF-1 signaling are now shown to contribute to retinal neovascularization, in part, by modulating the expression of various vascular mediators.

An anti-angiogenic state in mice and humans with retinal photoreceptor cell degeneration

Abnormal angiogenesis accompanies many pathological conditions including cancer, inflammation, and eye diseases. Proliferative retinopathy because of retinal neovascularization is a leading cause of blindness in developed countries. Another major cause of irreversible vision loss is retinitis pigmentosa, a group of diseases characterized by progressive photoreceptor cell degeneration. Interestingly, anecdotal evidence has long suggested that proliferative diabetic retinopathy is rarely associated clinically with retinitis pigmentosa. Here we show that neonatal mice with classic inherited retinal degeneration (Pdeb(rd1)/Pdeb(rd1)) fail to mount reactive retinal neovascularization in a mouse model of oxygen-induced proliferative retinopathy. We also present a comparable human paradigm: spontaneous regression of retinal neovascularization associated with long-standing diabetes mellitus occurs when retinitis pigmentosa becomes clinically evident. Both mouse and human data indicate that reactive retinal neovascularization either fails to develop or regresses when the number of photoreceptor cells is markedly reduced. Our findings support the hypothesis that a functional mechanism underlying this anti-angiogenic state is failure of the predicted up-regulation of vascular endothelial growth factor, although other growth factors may also be involved. Preventive and therapeutic strategies against both proliferative and degenerative retinopathies may emerge from this work.

Systemically expressed soluble Tie2 inhibits intraocular neovascularization

Retinal and choroidal neovascularization are the most frequent causes of severe and progressive vision loss. Studies have demonstrated that Tie2, an endothelial-specific receptor tyrosine kinase, plays a key role in angiogenesis. In this study, we determined whether adenovirus-mediated gene delivery of extracellular domain of the Tie2 receptor (ExTek) could inhibit experimental retinal and choroidal neovascularization. Immunofluorescence histochemistry with a monoclonal antibody to human Tie2 showed that Tie2 expression is prominent around and within the base of newly formed blood vessels of retinal and choroidal neovascular lesions. A single intramuscular injection of adenovirus expressing ExTek genes achieved plasma levels of ExTek exceeding 500 microg/ml in mice for 10 days (in neonates) and 7 days (in adults). This treatment inhibited retinal neovascularization by 47% (p < 0.05) in a murine model of ischemia-induced retinopathy. The same treatment reduced the incidence and extent of sodium fluorescein leakage from choroidal neovascular lesions by 52% (p < 0.05) and 36% (p < 0.01), respectively, in a laser-induced murine choroidal neovascularization model. The same mice showed a 45% (p < 0.001) reduction of integrated area of the choroidal neovascularization. These findings indicate that Tie2 signaling is a common component of the angiogenic pathway in both retinal and choroidal neovascularization, providing a potentially useful target in the treatment of intraocular neovascular diseases.

A short peptide domain of platelet factor 4 blocks angiogenic key events induced by FGF-2

Platelet factor 4 (PF-4) is a CXC-chemokine with strong anti-angiogenic properties. We have shown previously that PF-4 inhibits angiogenesis by associating directly with fibroblast growth factor 2 (FGF-2), inhibiting its dimerization, and blocking FGF-2 binding to endothelial cells. We now have characterized a small peptide domain (PF-447-70) derived from the C-terminus of PF-4, which conserves anti-angiogenic effects of the parent protein. PF-447-70 inhibited internalization of 125I-FGF-2 by endothelial cells in a time-dependent manner. The peptide reduced FGF-2-stimulated cell migration to control levels in wounded monolayers of bovine capillary endothelial cells. PF-447-70 also reduced FGF-2 induced phosphorylation of MAP kinases ERK-1 and ERK-2, which are essential for migration and survival of endothelial cells. In a serum-free ex vivo angiogenesis assay, the peptide blocked microvessel outgrowth by 89%. A single amino acid substitution within PF-447-70 abolished all inhibitory activities. To simulate a real anti-angiogenic treatment situation, we administered PF-447-70 systemically to mice implanted subcutaneously with FGF-2 containing gelatin sponges with the result of sparse, scattered, and immature vessel growth. The small peptide fragment derived from the angio-inhibitory CXC-chemokine PF-4 might be used as a starting point to develop anti-angiogenic designer drugs for angiogenesis-dependent pathologies such as cancer, diabetic retinopathy, and rheumatoid arthritis.

The bst locus on mouse chromosome 16 is associated with age-related subretinal neovascularization

Ocular neovascularization is the leading cause of blindness in developed countries and often causes rapid loss of vision in age-related macular degeneration. Acute visual loss is most often due to hemorrhage from new vessels that have extended from the choroid into the subretinal space. Growth of abnormal vessels beneath the retina in this condition is known as subretinal neovascularization (SRN). Age-related animal models of macular degeneration and SRN have not been described. Current animal models of SRN depend on chemical or physical stimuli to initiate growth of subretinal vessels. The genes responsible for age-related human macular degeneration with SRN have not been firmly identified. We report an angiogenic phenotype in Bst/+ mice that is age-related, clinically evident, and resembles human SRN. This represents a spontaneous, genetically determined model of SRN. Bst/+ mice offer the possibility of exploring the molecular mechanisms of SRN without the need for exogenous agents.

Thrombospondin-1, a natural inhibitor of angiogenesis, is present in vitreous and aqueous humor and is modulated by hyperglycemia

Negative regulators of angiogenesis play a major role in maintaining vascular homeostasis. Thrombospondin-1 (TSP1) is a natural inhibitor of angiogenesis. This report examines the presence of TSP1 in ocular samples and determines whether its production is altered in diabetes. Western blot analysis detected a 140 kDa antiangiogenic fragment of TSP1(gp140) in vitreous samples prepared from normal human and rat eyes. Intact TSP1 was detected in aqueous humor samples prepared from normal rat and bovine eyes. In contrast, TSP1 was virtually absent in vitreous and aqueous humor samples prepared from diabetic rat eyes. Furthermore, production of TSP1 by microvascular endothelial cells in culture was sensitive to high concentrations of glucose. Retinal blood vessels appeared nonuniform and dilated in diabetic animals when compared to control animals. These results demonstrate that TSP1 and its antiangiogenic fragment are present in aqueous humor and vitreous of normal rat eyes and are dramatically reduced in diabetes. Thus, TSP1 may play a role in ocular vascular homeostasis and its absence may contribute to vascular dysfunctions associated with diabetes.